There are several thousands of miles of submerged pipelines installed in the Gulf of Mexico and adjacent bays and in other submerged lands in which oil and gas production occurs. Many have a shore landing and many are in shallow coastal bays. While these lines are initially buried beneath the surface of the bottom, over time due to currents, storms and other forces the fill or overburden beneath which the lines are buried is disturbed so as to cause portions of the line to be exposed or part of the overburden to be shifted or removed. This has proven to be a dangerous condition because the exposed pipelines are subject to be hit and possibly ruptured by vessels navigating or fishing in shallow waters or being caught by anchors or nets drug along the bottom by fishing boats and particularly by shrimp trawls.
Since the pipelines carry hydrocarbons such as natural gas and/or oil at relatively high pressures, a break in the line can result in explosion or fire as well as the accidental discharge of oil and/or gas with adverse environmental consequences.
It is therefore desirable to periodically inspect the pipeline to determine whether any portion of the line is exposed or whether the overburden has been disturbed so that the pipeline is buried at a shallower depth then desired.
Apparatus is available for tracking submerged pipelines in relatively deep water, say at depths exceeding 10-12 feet. Such apparatus includes a Remote Operating Vehicle (R.O.V.) for carrying the magnetic sensors. This apparatus is tethered to a surface vessel and steered by remote control guidance means carried on the R.O.V. Such guidance means includes jet propulsion pumps and motors for raising and lowering the submarine as well as for turning it from side to side to steer it along the path of the pipeline at a desired distance off of the bottom. The sheer size of the submarine and its associated support equipment carried by the surface vessel renders operation in shallow water impractical, if not impossible. For example, the weight of the handling equipment for launching and retrieving the submarine from the surface vessel typically weights in excess of 20 tons and thus requires a large displacement vessel to carry such weight. The present invention however eliminates these disadvantages and provides means for tracking a pipeline buried in shallow water without the need for a large displacement vessel.
It is an object of the present invention to provide a submergible sled adapted to rest on the bottom for transporting an array of magnetic sensors for locating a submerged pipeline.
A further object of the present invention is a method of gathering data with electronic sensors by moving the sensor array laterally across the pipeline at longitudinally spaced points and gathering data with respect to the depth of the pipeline beneath the surface of the bottom at each pass and correlating the data from the longitudinally spaced points to determine the location of the pipeline with respect to the surface of the water bottom.